Adenosylhomocysteine hydrolase (E.C. 3.3.1.1) from calf liver has been purified to homogeneity by crystallization. It has a molecular weight of 237,500, and can be separated into two isoelectric focusing variants. When electrophoresed with sodium dodecyl sulfate, a major subunit of a molecular weight of 60,000 was found; five other minor subunit variants were also observed, with molecular weights ranging between 50,000 and 57,000. The presence of enzyme-bound NAD was confirmed, probably one NAD molecule bound/enzyme subunit. In addition to adenosine, 3-deazaadenosine was found to be an effective substrate as well as the direction of synthesis; but in the direction of hydrolysis, 3-deazaadenosine becomes a potent inhibitor. When tested in cell systems both 3-deazaadenosine and 5'-deoxy-5'-(isobutylthio)-3-deazaadenosine are effective antiviral agents. More, 3-deazaadenosine can also block chemotaxis by neutrophils and macrophages.